1. Field of the Invention
This invention relates to a dryer section apparatus for drying a web extending therethrough. More particularly, the present invention relates to an apparatus having a plurality of lower dryer drums and a plurality of upper dryer drums.
2. Information Disclosure Statement
When a formed web of paper emerges from a press section of a papermaking machine, the formed web still contains a large percentage of water therein. Much of this water is removed from the formed web during passage of the web through a drying section of the papermaking machine. Such dryer section usually includes a plurality of heated dryer drums over which the formed web extends. As the web is brought into intimate contact with the heated outer surface of the dryer drums, the web is heated so that at least a portion of the moisture contained therein is removed from the web.
The so-called "uni run" or "uno run" dryer sections typically include an upper and a lower tier of dryer drums. Each upper and lower tier comprise a plurality of heated, rotatable dryer drums. A felt extends in sinusoidal configuration alternately between dryer drums of the upper and lower tiers and the web is pressed into physical contact with the heated surface of each alternate dryer drum during passage through the dryer section. Although the aforementioned system provides support for the web by the felt during passage through the dryer section, such prior art systems suffer from the following disadvantages.
First, the web is brought into physical contact with only each alternate heated dryer drum during passage through the dryer section because each alternate dryer drum includes the supporting felt disposed between the heated surface of the dryer drum and the web. Secondly, as the web extends around the dryer drum with the felt disposed between the web and the heated surface of the dryer drum, there existed the tendency for the web to be thrown by centrifigal force and for the web to be detached from the felt due to the wedge of air pressure at the ingoing nip.
The present invention overcomes the aforementioned problems associated with the prior art arrangement by the provision of a unique configuration of upper and lower dryer drums. Unlike the prior art "uni run" system, the present invention provides a separate upper and lower felt with the upper felt extending alternately around an upper dryer drum and an upper intermediate roll in sinusoidal configuration. Similarly, the lower felt extends alternately between each lower dryer drum and a lower intermediate roll. The arrangement is such that each alternate intermediate roll of both the upper and lower intermediate rolls are wrapped by both the felt and the web. By such arrangement, the web extends in open draw between each adjacent upper and lower dryer drum so that the web passes in intimate contact with the heated surface of each upper and lower dryer drum. Furthermore, because of the aforementioned unique configuration, the unsupported distance travelled by the web between adjacent upper and lower dryer drums is kept to a minimum.
Therefore, the primary objective of the present invention is to provide a dryer section apparatus which overcomes the aforementioned inadequacies of the prior art devices and provides an apparatus which not only enables the formed web to come into intimate contact with the heated surface of each dryer drum, but also minimizes the open draw between adjacent upper and lower dryer drums.
Another object of the present invention is the provision of a dryer section apparatus in which each lower intermediate roll is disposed between adjacent lower dryer drums such that each alternate lower intermediate roll guides both the web and the lower felt.
Another object of the present invention is the provision of a dryer section apparatus in which each upper intermediate roll of a plurality of upper intermediate rolls is disposed between adjacent upper dryer drums such that each alternate upper intermediate roll guides both the web and the felt so that the web is transferred in open draw between adjacent upper and lower dryer drums, thereby minimizing the length of the open draw and inhibiting web flutter during transfer between upper and lower dryer drums.
Another object of the present invention is the provision of a dryer section apparatus in which the upper and lower intermediate rolls are vacuum rolls.
Another object of the present invention is the provision of a dryer section apparatus in which each of the upper and lower intermediate rolls is a grooved roll.
Another object of the present invention is the provision of a dryer section apparatus in which each lower intermediate roll which guides both the web and the felt is disposed at a first distance relative to the upper intermediate roll which is partially wrapped by only the upper felt. Each of the lower intermediate rolls which are partially wrapped by the lower felt only are disposed a second distance relative to the adjacent upper intermediate roll partially wrapped by both the web and the upper felt and the second distance is the same as, or greater than the first distance.
Another object of the present invention is the provision of a dryer section apparatus in which each intermediate roll which is partially wrapped by the felt and the web defines a pocket, a blow box being disposed within each of the pockets for ventilating each pocket and for removing boundary air entering into the pocket.
Another object of the present invention is the provision of a dryer section apparatus including a plurality of doctor blades with each blade cooperating with a corresponding dryer drum of the upper and lower dryer drums such that each blade contacts an unwrapped surface of each respective drum.
Another object of the present invention is the provision of a dryer section apparatus in which the doctor blades assist in stabilizing the web by restricting the influence of external air flow. The blades also assist in directing a tail of the web during threading of the apparatus without the use of ropes.
Another object of the present invention is the provision of a dryer section apparatus including a duct which is disposed adjacent to each lower intermediate roll which is partially wrapped only by the lower felt. The duct blows air through the lower felt for ventilating the adjacent dryer pocket defined between the upper and lower felts.
Another object of the present invention is the provision of a dryer section apparatus which includes ventilating means disposed adjacent to each upper intermediate roll partially wrapped only by the upper felt, the ventilating means blowing air through the upper felt for ventilating air from an adjacent dryer pocket defined between the upper and lower felts.
Other objects and advantages of the present invention will be evident to those skilled in the art by consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.